In a switching system such as described in European Patent Application published under N.degree. 0 387 464, messages are exchanged between data processing units, thru bursts comprising a fixed number of bytes. The switching system performs an optimized number of simultaneous transfers of data between pairs of units comprising an origin unit and a target unit selected among a plurality of data processing units attached to the switching system. Each unit includes a set of outbound queues with one outbound queue associated with each one of the data processing units to which it may sent data packets or messages, for storing the data packets to be sent by the data processing unit to the data processing unit associated with said one outbound queue.
The transfers are performed by a data switch during a burst time under control of switching control signals sent to the data switch by the selected units in response to control out signals generated by a scheduler during a previous burst time. The scheduler runs a selection algorithm which gives each unit an equal chance to be selected as origin unit and/or target unit in a given period.
It results from this switching concept, that the messages are transferred as a succession of bursts comprising a fixed number of bytes for example 32 bytes. Interleaved bursts of messages from/to different origin/target units are provided to the switching system, and the data bursts are switched with an associated control field comprising control information relative to the burst contents such as First burst/Last burst/Byte count. The data bursts and associated control information are exchanged on separate media.
The message exchanges must be protected against any alterations. To do so an error correction code which maybe of a cyclic redundancy code CRC, must be included into each message. In conventional applications, the maximum message size is 64 kilobytes, thus a 19-bit CRC is needed to provide for an efficient detection of all types of bit sequence error.
As usual, the error correction code CRC could be added at the end of the message, but due to the slicing of the messages into bursts, this would lead to a complicated handling of the CRC, namely an additional burst at the end of the message would be needed to include the CRC bits and this would results in a too high overhead in case of one burst messages.